fix: add missing checks to several API and web handlers (#39501) (#39507)

Backport #39501 by @silverwind

Several handlers skipped checks that their sibling routes or settings
already enforce. This brings them in line.

- Push mirror API honors `DISABLE_NEW_PUSH` and checks the caller's
permission
- Media API serves small files with the usual content headers
- Issue attachment API ignores comment attachments
- Push-to-create respects `FORCE_PRIVATE`
- Profile feeds and follow actions respect `ENABLE_FEED` and owner
visibility
- Tag delete route refuses release tags
- Refresh token grant only accepts refresh tokens
- Gitea migrations bound the source's page size

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: bircni <bircni@icloud.com>

routers/web/auth/oauth2_provider.go

@@ -576,7 +576,7 @@ func handleRefreshToken(ctx *context.Context, form forms.AccessTokenForm, server
 	}
 
 	token, err := oauth2_provider.ParseToken(form.RefreshToken, serverKey)
-	if err != nil {
+	if err != nil || token.Kind != oauth2_provider.KindRefreshToken {
 		handleAccessTokenError(ctx, oauth2_provider.AccessTokenError{
 			ErrorCode:        oauth2_provider.AccessTokenErrorCodeUnauthorizedClient,
 			ErrorDescription: "unable to parse refresh token",